There are so many garden pests and diseases it can seem an overwhelming task to figure out which one is causing trouble for your plants. If the leaves on your plants are turning silver, it could be due to feeding injury caused by the thrip. Using a combination of control techniques should help you keep this common insect pest under control.
Thrips are very small, only about 1/25 inch long. They are slender with two pairs of narrow wings fringed with fine hairs. Adult thrips vary in colour from pale yellow to brown. Eggs are bean shaped and translucent. Just after hatching nymphs are also translucent but eventually turn yellowish. They are only about 1/50-inch long. During pre-pupa and pupa stages, nymphs are motionless and develop their wings.
Adults insert about 100 eggs into leaf tissue and they will hatch in about three days. Nymphs will feed for about four or five days and then drop to the soil to pupate and become adults. After about two days adults emerge from the soil. The exact time it takes for life cycle completion depends on temperatures and the type of thrip. Adults will overwinter in plant debris before laying eggs in the spring.
Although thrips are attracted to pollen, they primarily feed on leaves. They use rasping and sucking mouth parts to feed on the inner parts of leaves. Small populations can cause fine stippling. When large populations occur, leaves take on a silvery look. Thrips are very small and can be difficult to see. If you shake foliage gently you should see them move around on leaves. According to Virginia Tech University, thrips can transmit harmful viruses.
Keep gardens weed-free, as thrips often host on weeds. Washing plants off with a strong jet of water from the hose can knock off and kill many thrips. Thrips overwinter in crop debris, so remove and destroy all debris after the season is over. Plants are particularly susceptible in June and July so control weeds and keep plants properly irrigated during these months. Unhealthy plants are more susceptible to pest infestation. If pesticides are necessary, thoroughly coat plants as thrips can hide in crevices and be difficult to reach with chemicals.